Filler tubes for optical communication cable construction

ABSTRACT

An optical communication cable includes a central strength member, at least one optical fiber, a buffer tube surrounding the at least one optical fiber; and at least one non-solid filler tube defining a cavity, wherein the cavity contains a water-blocking component and no optical fibers, and wherein the buffer tube and the filler tube are stranded about the central strength member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 62/151,724, filed on Apr. 23, 2015, and is incorporatedherein by reference.

BACKGROUND

The disclosure relates generally to materials for the manufacture offiber optic communication cables and more specifically to the use ofnon-solid filler tubes in the construction of an optical fibercommunication cable. Historically, solid filler rods have been used forstranded cable designs when not all of the buffer tube positions in anoptical cable are needed. Conventional rods may be formed from a solidor foamed polyethylene (PE) material to have the same diameter along thelongitudinal length of the rod as the live tubes they are replacing. Insome designs, the solid or foamed tubes may contain recycled or regroundPE.

Advances in the construction of optical communication cables are drivingnew approaches to the use of filler tubes in loose tube and/or strandedcable design. For example, maximum lengths for certain conventionalloose tube cables may be around 14 km, and filler tubes or rods can bespliced into the process mid-run so that remnant scrap lengths arealmost eliminated. However, binder yarns which typically hold thestranded core together are being replaced by a thin extruded layer of PEfilm in some cable designs and the desire for much longer productionruns are driving a line that cannot now stop mid-run due to theextrusion process. These changes, along with the desire for runs up to30 km, for example, and the inability to splice filler rods togetherduring a run, have implications for filler rods. For opticalcommunication cables manufactured in accordance with these newprocesses, it is desirable to use non-solid filler tubes formed from amaterial other than PE, for example, to prevent the filler tubes fromsticking to the PE film. Also, because of the longer production runs andthe inability to splice in fillers, order-to-length filler tubes may bepreferable in the construction of cables having buffer tubes that aresometimes replaced by filler rods due to fiber counts or fiber placementnot requiring use of all the live positions in the cable.

SUMMARY

Aspects of the present disclosure relates to an optical fibercommunication cable that includes at least one non-solid filler tube toreplace the solid rods conventionally used as fillers in stranded cabledesigns. The filler tube may be formed from a polypropylene (PP)compound. However, any other plastic including PE, polycarbonate (PC),polybutylene terephthalate (PBT), etc. may be used depending onrequirements of other stranded cable products.

In accordance with other aspects of the present disclosure, an opticalcommunication cable may include a central strength member, at least oneoptical fiber, a buffer tube surrounding the at least one optical fiber,and at least one non-solid filler tube defining a cavity, wherein thecavity contains a water-blocking component and no optical fibers, andwherein the buffer tube and the filler tube are stranded about thecentral strength member.

In accordance with yet other aspects of the present disclosure, a methodof manufacturing an optical communication cable comprises extruding afiller tube from a plastic compound using a tip and die to define acavity by generating an annular cross section having an inner diameterand an outer diameter, feeding a water blocking component into thecavity through a crosshead in the tip, and stranding the filler tubecontaining no optical fibers with at least one other core element arounda central strength element.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and theoperation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an optical fiber cable, inaccordance with aspects of the present disclosure;

FIG. 2 is a cross-sectional view of a non-solid filler tube, inaccordance with aspects of the present disclosure;

FIG. 3 is a table illustrating the effects of thermal cycling on twelvefiber gel free loose tube cables having solid and non-solid fillercomponents, in accordance with aspects of the present disclosure; and

FIG. 4 is a chart illustrating cable integrity during installation oftwelve fiber gel free loose tube cables having solid and non-solidfiller components, in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Referring generally to the figures, various embodiments of anarrangement of storing fiber optic filler tubes are shown. In general,many fiber optic cables include one or more buffer tubes, for exampleloose buffer tubes. The buffer tubes typically are a hollowthermoplastic tube with a central bore that contains one or more opticalfibers and stranded around a central strength member. In someembodiments, one or more buffer tubes may not need to include opticalfibers. However, to maintain the shape of the cable and the mechanicalproperties of the cable, filler tubes in accordance with aspects of thisinvention may be used in the place of those buffer tubes that wouldotherwise be empty. Following stranding of the buffer tubes and thefiller tubes, additional layers (e.g., binders, water block tape, armorlayers) may be formed around the stranded buffer tubes and finally acable jacket is applied to the cable. Cable formation is a continuousprocess in which buffer tubes are drawn or paid out as the buffer tubesor filler tubes are wrapped around a central strength member in astranding pattern. In some embodiments, the stranded buffer tubes orfiller tubes may be taken up and stored on a reel prior to applicationof additional outer cable layers, such as an armor layer, water blocklayers and cable jacket.

Referring to FIG. 1, a cable in the form of a fiber optic cable 110 maybe an outside-plant loose tube cable, an indoor cable withfire-resistant/retardant properties, an indoor/outdoor cable, or anothertype of cable, such as a datacenter interconnect cable withmicro-modules or a hybrid fiber optic cable including conductiveelements. According to an exemplary embodiment, the cable 110 includes acore 112 (e.g., sub-assembly, micro-module), which may be located in thecenter of the cable 110 or elsewhere and may be the only core of thecable 110 or one of several cores. According to an exemplary embodiment,the core 112 of the cable 110 includes core elements 114.

In some embodiments, the core elements 114 include a tube 116, such as abuffer tube surrounding at least one optical transmission element 118, atight-buffer surrounding an optical fiber, or other tube. According toan exemplary embodiment, the tube 116 may contain two, four, six,twelve, twenty-four or other numbers of optical fibers 118. Incontemplated embodiments, the core elements 114 additionally oralternatively include a tube 116 in the form of a dielectric insulatorsurrounding a conductive wire or wires, such as for a hybrid cable.

In some embodiments, the tube 116 further includes a water-blockingelement, such as gel (e.g., grease, petroleum-based gel) or an absorbentpolymer (e.g., super-absorbent polymer particles or powder). In somesuch embodiments, the tube 116 includes yarn 120 carrying (e.g.,impregnated with) super-absorbent polymer, such as at least onewater-blocking yarn 120, at least two such yarns, or at least four suchyarns per tube 116. In other contemplated embodiments, the tube 116includes super-absorbent polymer without a separate carrier, such aswhere the super-absorbent polymer is loose or attached to interior wallsof the tube. In some such embodiments, particles of super-absorbentpolymer are partially embedded in walls of the tube 116 (interior and/orexterior walls of the tube) or bonded thereto with an adhesive. Forexample, the particles of super-absorbent polymer may be pneumaticallysprayed onto the tube 116 walls during extrusion of the tube 116 andembedded in the tube 116 while the tube 116 is tacky, such as fromextrusion processes.

According to an exemplary embodiment, the optical fiber 118 of the tube116 is a glass optical fiber, having a fiber optic core surrounded by acladding (shown as a circle surrounding a dot in FIG. 1). Some suchglass optical fibers may also include one or more polymeric coatings.The optical fiber 118 of the tube 116 is a single mode optical fiber insome embodiments, a multi-mode optical fiber in other embodiments, amulti-core optical fiber in still other embodiments. The optical fiber118 may be bend resistant (e.g., bend insensitive optical fiber, such asCLEARCURVE™ optical fiber manufactured by Corning Incorporated ofCorning, N.Y.). The optical fiber 118 may be color-coated and/ortight-buffered. The optical fiber 118 may be one of several opticalfibers aligned and bound together in a fiber ribbon form.

According to an exemplary embodiment, the core 112 of the cable 110includes a plurality of additional core elements (e.g., elongateelements extending lengthwise through the cable 110), in addition to thetube 116, such as at least three additional core elements, at least fiveadditional core elements. According to an exemplary embodiment, theplurality of additional core elements includes at least one of a fillertube 122 and/or an additional tube 116′. In other contemplatedembodiments, the core elements 114 may also or alternatively includestraight or stranded conductive wires (e.g., copper or aluminum wires)or other elements. In some embodiments, the core elements are all aboutthe same size and cross-sectional shape (see FIG. 1), such as all beinground and having diameters of within 10% of the diameter of the largestof the core elements 114. In other embodiments, core elements 114 mayvary in size and/or shape.

The cable 110 includes a binder film 126 (e.g., membrane) surroundingthe core 112, exterior to some or all of the core elements 114. The tube116 and the plurality of additional core elements 116′, 122 are at leastpartially constrained (i.e., held in place) and directly or indirectlybound to one another by the binder film 126. In some embodiments, thebinder film 126 directly contacts the core elements 114. For example,tension T in the binder film 126 may hold the core elements 114 againsta central strength member 124 and/or one another. The loading of thebinder film 126 may further increase interfacial loading (e.g.,friction) between the core elements 114 with respect to one another andother components of the cable 110, thereby constraining the coreelements 114.

According to an exemplary embodiment, the binder film 126 includes(e.g., is formed from, is formed primarily from, has some amount of) apolymeric material such as polyethylene (e.g., low-density polyethylene,medium density polyethylene, high-density polyethylene), polypropylene,polyurethane, or other polymers. In some embodiments, the binder film126 includes at least 70% by weight polyethylene, and may furtherinclude stabilizers, nucleation initiators, fillers, fire-retardantadditives, reinforcement elements (e.g., chopped fiberglass fibers),and/or combinations of some or all such additional components or othercomponents.

According to an exemplary embodiment, the binder film 126 is formed froma material having a Young's modulus of 3 gigapascals (GPa) or less,thereby providing a relatively high elasticity or springiness to thebinder film 126 so that the binder film 126 may conform to the shape ofthe core elements 114 and not overly distort the core elements 114,thereby reducing the likelihood of attenuation of optical fibers 118corresponding to the core elements 114. In other embodiments, the binderfilm 126 is formed from a material having a Young's modulus of 5 GPa orless, 2 GPa or less, or a different elasticity, which may not berelatively high.

According to an exemplary embodiment, the binder film 126 is thin, suchas 0.5 mm or less in thickness (e.g., about 20 mil or less in thickness,where “mil” is 1/1000th inch). In some such embodiments, the film is 0.2mm or less (e.g., about 8 mil or less), such as greater than 0.05 mmand/or less than 0.15 mm. In some embodiments, the binder film 126 is ina range of 0.4 to 6 mil in thickness, or another thickness. Incontemplated embodiments, the film may be greater than 0.5 mm and/orless than 1.0 mm in thickness. In some cases, for example, the binderfilm 126 has roughly the thickness of a typical garbage bag. Thethickness of the binder film 126 may be less than a tenth the maximumcross-sectional dimension of the cable, such as less than a twentieth,less than a fiftieth, less than a hundredth, while in other embodimentsthe binder film 126 may be otherwise sized relative to the cablecross-section. In some embodiments, when comparing averagecross-sectional thicknesses, the jacket 134 is thicker than the binderfilm 126, such as at least twice as thick as the binder film 126, atleast ten times as thick as the binder film 126, at least twenty timesas thick as the binder film 126. In other contemplated embodiments, thejacket 134 may be thinner than the binder film 126, such as with a 0.4mm nylon skin-layer jacket extruded over a 0.5 mm binder film.

The thickness of the binder film 126 may not be uniform around the boundstranded elements 114. As such, the “thickness” of the binder film 126,as used herein, is an average thickness around the cross-sectionalperiphery. Use of a relatively thin binder film 126 allows for rapidcooling of the binder film 126 during manufacturing and thereby allowingthe binder film 126 to quickly hold the core elements 114 in place, suchas in a particular stranding configuration, facilitating manufacturing.By contrast, cooling may be too slow to prevent movement of the strandedcore elements when extruding a full or traditional jacket over the core,without binder yarns (or the binder film); or when even extruding arelatively thin film without use of a caterpuller or other assistingdevice. However such cables are contemplated to include coextrudedaccess features, embedded water-swellable powder, etc. Subsequent to theapplication of the binder film 126, the manufacturing process mayfurther include applying a thicker jacket 134 to the exterior of thebinder film 126, thereby improving robustness and/or weather-ability ofthe cable 110. In other contemplated embodiments, the core 112,surrounded by the binder film 114, may be used and/or sold as a finishedproduct.

Still referring to FIG. 1, the cable 110 further includes the centralstrength member 124, which may be a dielectric strength member, such asan up-jacketed glass-reinforced composite rod. In other embodiments, thecentral strength member 124 may be or include a steel rod, strandedsteel, tensile yarn or fibers (e.g., bundled aramid), or otherstrengthening materials. As shown in FIG. 1, the central strength member124 includes a center rod 128 and is up-jacketed with a polymericmaterial 130 (e.g., polyethylene, low-smoke zero-halogen polymer).

As shown in FIG. 2, the filler tube 122 in accordance with aspects ofthe present disclosure may be a non-solid tube having an outer diameter124 defined by the live tube which it is replacing. The tube innerdiameter 126 should provide a wall thickness which provides sufficientcrush strength for the filler tube. For example, for a filler tube 122comprised of PP, 2.5 mm OD and 1.6 mm ID provides sufficient crushstrength for the filler tube. The filler tube 122 may be comprised ofPP, PE, PC/PBT, or any other suitable polymer material to provide themechanical properties necessary. The tube wall defines an inner cavity128 that may be filled with water blocking components, such as SAPpowder, SAP coated yarn, gel or other suitable water blockingcomponents.

The filler tube 122 may be manufactured by extruding the desired plasticcompound compatible with the relevant cable design (PE, PP, PC, PBT, orany other suitable plastic, or combination of plastics) using a tip anddie to generate an annular cross section with the desired dimensions.The water blocking component may be fed through the crosshead inside thetip. A yarn may be fed into the process through the crosshead. SAPpowder may be blown in to the tip through the crosshead (process coveredby existing Corning patent), or water blocking gel may be pumped intothe cross head.

The extrusion line process parameters should be established to minimizepost extrusion shrinkage in the filler tube, and to maintain the desiredround geometry. For example the filler tube 122 must be sufficientlycooled by water trough or other cooling mechanism before being exposedto sheaves or other equipment touch points such that the tube is intolerance for diameter and ovality. In addition the cooling rate afterthe extruder and before the take-up must be provided to controlshrinkage of the tube after extrusion within desired specifications.

A cable with filler tubes such as that shown in FIGS. 1-2 has betterattenuation performance at low temperatures than does a cable withfiller rods. Thermal expansion coefficient for a cable design can beestimated by the equation:

α_(eff) =Σ E _(i) A _(i)α_(i) /Σ E _(i) A _(i),

where E is modulus, A is cross sectional area, and α is the coefficientof thermal expansion, and the summations are made across all theelements in the cable design. A cable design with non-solid filler tubescompared to a design with solid rods will have a comparatively lowerα_(eff) due to less cross sectional area of these elements, and it willtherefore contract less at low temperatures. An experiment was run toconfirm this benefit of filler tubes (blank tubes) compared to solidrods. FIG. 3 is a table illustrating a comparison of 12 fiber gel freeloose tube cable performance at 1550 nm.

The cable integrity during installation may be improved as a result ofusing the non-solid filler tubes 122 in the cable. A cable test,sometimes referred to as the Wringer test, has been devised to simulateextreme tension and bend radius conditions which a cable may be exposedto during installation. As shown in FIG. 4, various loads are applied toa cable as it is respooled across a variety of sheave sizes. The cablesare then measured for fiber breaks. A probability curve of fiber breaksacross various T/r (tension over radius) levels is generated. Cabletesting was performed on the same 12 fiber cables discussed above andshown in FIG. 3. Wringer performance in the cable with the non-solidfiller tubes 122 was better than in the cable with the solid rods. Asillustrated in FIG. 4, the rigid, solid rods create more localizedstresses when load is applied at increasingly small diameters whichresults in more broken fibers.

Today, many filler rods are foamed to decrease the amount of plasticmaterial required, and thus reduce the cost of the filler. In addition,some manufacturers will use a percentage of regrind or recycled materialto lower the cost of the filler rod. By moving to a non-solid,non-foamed filler tube 122 with water blocking components, the requiredamount of plastic can be further reduced resulting in significantmaterial cost savings. Some water blocking components such as superabsorbent polymer (SAP), or a yarn coated with SAP are inexpensiverelative to the plastic compound, and so filling the void with one ofthese materials is a cheaper alternative than a solid foamed rod, andmuch cheaper than a solid non-foamed rod.

While the specific cable embodiments discussed herein and shown in thefigures relate primarily to cables and core elements that have asubstantially circular cross-sectional shape defining substantiallycylindrical internal bores, in other embodiments, the cables and coreelements discussed herein may have any number of cross-section shapes.

The optical transmission elements discussed herein include opticalfibers that may be flexible, transparent optical fibers made of glass orplastic. The fibers may function as a waveguide to transmit lightbetween the two ends of the optical fiber. Optical fibers may include atransparent core surrounded by a transparent cladding material with alower index of refraction. Light may be kept in the core by totalinternal reflection. Glass optical fibers may comprise silica, but someother materials such as fluorozirconate, fluoroaluminate andchalcogenide glasses, as well as crystalline materials such as sapphire,may be used. The light may be guided down the core of the optical fibersby an optical cladding with a lower refractive index that traps light inthe core through total internal reflection. The cladding may be coatedby a buffer and/or another coating(s) that protects it from moistureand/or physical damage. These coatings may be UV-cured urethane acrylatecomposite materials applied to the outside of the optical fiber duringthe drawing process. The coatings may protect the strands of glassfiber.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modifications,combinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An optical communication cable comprising: acentral strength member; a plurality of core elements stranded about thestrength member, wherein the plurality of core elements includes atleast one non-solid filler tube defining a cavity, the cavity containinga water-blocking component and no optical fibers.
 2. The opticalcommunication cable of claim 1, wherein the plurality of core elementsfurther includes at least one buffer tube, the at least one buffer tubesurrounding at least one optical transmission element.
 3. The opticalcommunication cable of claim 1, wherein the water-blocking component isa gel, a super-absorbent polymer powder, or a super-absorbent polymeryarn.
 4. The optical communication cable of claim 1, wherein each coreelement of the plurality of core elements has an outside diameter within10% of an outside diameter of each other core element in the pluralityof core elements.
 5. The optical communication cable of claim 1, whereina binder film surrounds the plurality of core elements such that eachcore element is at least partially constrained and directly orindirectly bound to each other core element by the binder film.
 6. Theoptical communication cable of claim 1, wherein the filler tubecomprises a wall having an inner diameter of at least 1.6 millimetersand an outer diameter of at least 2.5 millimeters.
 7. The opticalcommunication cable of claim 1, wherein the filler tube is an extrudedpolymer tube that comprises polypropylene, polyethylene, polycarbonate,or polybutylene terephthalate.
 8. The optical communication cable ofclaim 1, wherein the central strength member is up-jacketed with apolymeric material.
 9. The optical communication cable of claim 8,wherein the central strength member is dielectric.
 10. The opticalcommunication cable of claim 9, wherein the central strength member is aglass-reinforced composite rod.
 11. A method of manufacturing an opticalcommunication cable comprising: extruding a filler tube from a plasticcompound using a tip and die to define a cavity by generating an annularcross section having an inner diameter and an outer diameter; feeding awater blocking component into the cavity through a crosshead in the tip;and stranding the filler tube containing no optical fibers with at leastone other core element around a central strength element.
 12. The methodof claim 11, wherein the at least one other core element includes atleast one buffer tube, the method further comprising providing at leastone optical transmission element in the at least one buffer tube. 13.The method of claim 11, wherein the water-blocking component is a gel, asuper-absorbent polymer powder, or a super-absorbent polymer yarn. 14.The method of claim 11, further comprising forming the filler tube suchthat the outer diameter is sized to be within 10% of an outside diameterof the at least one other core element.
 15. The method of claim 11,further comprising surrounding the stranded filler tube and the at leastone other core element with a binder film such that the stranded fillertube and the at least one other core element are at least partiallyconstrained and bound by the binder film.
 16. The method of claim 11,wherein the inner diameter of the filler tube is at least 1.6millimeters and the outer diameter of the filler tube is at least 2.5millimeters.
 17. The method of claim 11, wherein the plastic compoundcomprises polypropylene, polyethylene, polycarbonate, or polybutyleneterephthalate.
 18. The method of claim 11, further comprising upjacketing the central strength member with a polymeric material.
 19. Themethod of claim 18, wherein the central strength member is dielectric.20. The method of claim 19, wherein the central strength member is aglass-reinforced composite rod.